twat

Unknown origin. Obsolete by the mid-eighteenth century; revived by Robert Browning in his 1841 Pippa Passes; he had misunderstood a rhyme from 1660 that went "they talk’t of his having a Cardinall’s Hat / they’d send him as soon an Old Nun’s Twat" and thought "twat" denoted part of a nun's habit. For more, see Wikipedia.